[Bug 1812752] Re: UX: changing GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub has no effect in cloud images

[Julian Andres Klode]

Yes I forgot the option existed and didn't have the context while
writing the comment, but generally speaking debconf is a crapshoot and
while it is there and it makes sense to use it accordingly, we certainly
should try to avoid introducing more of it.

The file here is a mess, so it's a conffile and the I believe preinst
merges the previously configured value into the new file such that you
only get promoted about differences in other options, very annoying, and
highly fragile.

You can easily see this doesn't scale to every possible grub option.

Presumably we should introduce /usr/lib/grub/default.d and implement the
whole drop in logic with /usr directories which is a goal certainly for
all our packages.

Then again it is 2024, and people now are highly used to settings made
in foo being overriden by settings in foo.d as that's the standard
semantic for a wide range of packages, most prominently systemd, so I
don't think this is as much of a concern as it was 5 years ago.

That being said, of course not mentioning that grub.d exists and
overrides settings in the default configuration file is an oversight
that certainly should be fixed.

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https://bugs.launchpad.net/bugs/1812752

Title:
  UX: changing GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub has no
  effect in cloud images

Status in cloud-images:
  New
Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  I need to modify the kernel command line, such as to work around bug
  1573095. I edit GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub and
  rerun update-grub but this has no effect.

  The reason is that this is redefined in
  /etc/default/grub.d/50-cloudimg-settings.cfg and that one overrides
  /etc/default/grub. I was misled by the comment in /etc/default/grub
  and information widely available on the Internet that editing
  /etc/default/grub is sufficient, and looked no further.

  I understand the reason for not modifying /etc/default/grub in cloud
  image builds (to avoid future conffile prompts) and I'm not suggesting
  that it should be modified. To fix this UX issue properly I think the
  grub package needs to provide a mechanism that allows cloud image
  builds to override the default without dropping in an overriding file
  (or for that override file to be the sole place that users need to
  look).

  This affects grub2 2.02-2ubuntu8.9 from Bionic cloud image build
  20190114 for example.

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